Session Management Method, Interworking Method, and Network Apparatus

1. A method, comprising: when establishing a guaranteed bit rate (GBR) flow of a terminal device in a fifth generation (5G) communications system, determining, by a session management network element in the 5G communications system based on a quality of service (QoS) parameter and an operator policy, that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to a fourth generation (4G) communications system, wherein determining that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to the 4G communications system comprises determining that a service type corresponding to the GBR flow is a service type supported by an operator policy of the 4G communications system; and establishing, by the session management network element for the GBR flow, a session context corresponding to the 4G communications system, wherein establishing the session context corresponding to the 4G communications system comprises establishing a bearer ID in the 4G communications system for the GBR flow.

2. The method according to claim 1 , further comprising: sending, by the session management network element to an access and mobility management function (AMF) network element, information for allocating the bearer ID in the 4G communications system for the GBR flow; and obtaining, by the session management network element from the AMF network element, the bearer ID allocated by the AMF network element; wherein the session context comprises the bearer ID.

3. The method according to claim 2 , further comprising: allocating, by the session management network element, a QoS parameter in the 4G communications system for the GBR flow; wherein the session context further comprises the QoS parameter in the 4G communications system.

4. The method according to claim 1 , further comprising: determining, by the session management network element, that the GBR flow needs to be established.

5. The method according to claim 1 , wherein the method further comprises: receiving, by the session management network element, policy and charging control (PCC) rule information from a policy control network element, the PCC rule information comprising a PCC rule that is of the GBR flow and that corresponds to the 4G communications system, the PCC rule comprising the QoS parameter.

6. An apparatus in a fifth generation (5G) communications system, comprising: a memory storage comprising instructions; and one or more processors in communication with the memory, wherein the one or more processors are configured to execute the instructions to facilitate the following being performed by the apparatus: when establishing a guaranteed bit rate (GBR) flow of a terminal device in the 5G communications system, determining, based on a quality of service (QoS) parameter and an operator policy, that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to a fourth generation (4G) communications system, wherein determining that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to the 4G communications system comprises determining that a service type corresponding to the GBR flow is a service type supported by an operator policy of the 4G communications system; and establishing a session context corresponding to the 4G communications system for the GBR flow, wherein establishing the session context corresponding to the 4G communications system comprises establishing a bearer ID in the 4G communications system for the GBR flow.

7. The apparatus according to claim 6 , wherein the one or more processors are further configured to execute the instructions to facilitate the following being performed by the apparatus: sending, to an access and mobility management function (AMF) network element, information for allocating the bearer ID in the 4G communications system for the GBR flow; and obtaining, from the AMF network element, the bearer ID allocated by the AMF network element; wherein the session context comprises the bearer ID.

8. The apparatus according to claim 7 , wherein the one or more processors are further configured to execute the instructions to facilitate the following being performed by the apparatus: allocating a QoS parameter in the 4G communications system for the GBR flow; wherein the session context further comprises the QoS parameter in the 4G communications system.

9. The apparatus according to claim 6 , wherein the one or more processors are further configured to execute the instructions to facilitate the following being performed by the apparatus: determining that the GBR flow needs to be established.

10. A method, comprising: when establishing a guaranteed bit rate (GBR) flow of a terminal device in a fifth generation (5G) communications system, determining, by a session management network element in the 5G communications system based on a quality of service (QoS) parameter and an operator policy, that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to a fourth generation (4G) communications system, wherein determining that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to the 4G communications system comprises determining that a service type corresponding to the GBR flow is a service type supported by an operator policy of the 4G communications system; sending, by the session management network element to an access and mobility management function (AMF) network element, information for allocating a bearer ID in the 4G communications system for the GBR flow; allocating, by the AMF network element, the bearer ID for the GBR flow; and obtaining, by the session management network element from the AMF network element, the bearer ID allocated by the AMF network element.

11. The method according to claim 10 , further comprising: establishing, by the session management network element for the GBR flow, a session context corresponding to the 4G communications system, the session context comprising the bearer ID.

12. The method according to claim 11 , further comprising: allocating, by the session management network element, a QoS parameter in the 4G communications system for the GBR flow; wherein the session context further comprises the QoS parameter in the 4G communications system.

13. The method according to claim 10 , further comprising: determining, by the session management network element, that the GBR flow needs to be established.

14. A fifth generation (5G) communications system, comprising: a session management network element; and an access and mobility management function (AMF); wherein the session management network element is configured to: when establishing a guaranteed bit rate (GBR) flow of a terminal device in the 5G communications system, determine, based on a quality of service (QoS) parameter and an operator policy, that the GBR flow is a GBR flow required for handing over the terminal device from the first communications system to a fourth generation (4G) communications system, wherein determining that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to the 4G communications system comprises determining that a service type corresponding to the GBR flow is a service type supported by an operator policy of the 4G communications system; and send, to the AMF network element, information for allocating a bearer ID in the 4G communications system for the GBR flow; wherein the AMF network element is configured to allocate the bearer ID for the GBR flow; and wherein the session management network element is further configured to obtain the bearer ID allocated by the AMF network element.

15. The 5G communications system according to claim 14 , wherein the session management network element is further configured to establish for the GBR flow a session context corresponding to the 4G communications system, the session management network element establishing the session context for the GBR flow, the session context comprising the bearer ID.

16. The 5G communications system according to claim 15 , wherein the session management network element is further configured to allocate a QoS parameter in the 4G communications system for the GBR flow, the session context further comprising the QoS parameter in the 4G communications system.

17. The 5G communications system according to claim 14 , wherein the session management network element is further configured to determine that the GBR flow needs to be established.

18. A non-transitory computer-readable medium having processor-executable instructions stored thereon, wherein the processor-executable instructions, when executed, facilitate: when establishing a guaranteed bit rate (GBR) flow of a terminal device in a fifth generation (5G) communications system, determining, by a session management network element in the 5G communications system based on a quality of service (QoS) parameter and an operator policy, that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to a fourth generation (4G) communications system, wherein determining that the GBR flow is a GBR flow required for handing over the terminal device from the 5G communications system to the 4G communications system comprises determining that a service type corresponding to the GBR flow is a service type supported by an operator policy of the 4G communications system; and establishing, by the session management network element for the GBR flow, a session context corresponding to the 4G communications system, wherein establishing the session context corresponding to the 4G communications system comprises establishing a bearer ID in the 4G communications system for the GBR flow.